*2.1.2 Tropical areas vs. temperate areas*

All the successes in tropical areas were strengthened by the fact that initial biological control successes occurred on tropical islands. Success is the consequence of latitude and is reinforced on a physiological basis that is explained comparing the Heterodynamous insects and Homodynamous insects as below:

	- a.are unable to continuously reproduce throughout year.
	- b.generally have disconnected generations, i.e., all their stages may not be present at any one time.
	- c. require conjunction between natural enemy and pest.
	- a.are capable to reproduce throughout year.
	- b.have synchronized or connected generations and all their stages may be present at any one time.
	- c. are easiest species to control with biological method.

## **2.2 Introduction strategies**

## *2.2.1 Pros and Cons of multiple introductions*

	- a.Parasitization of host (with overlapping generations) giving rise to disconnected generations because of the eliminated host stage.
	- b.Parasitization of host by incapable parasitoid that may lead to reduced intraspecific competition between individuals of the host species at high densities.
	- a.Enhanced effective biological control may be achieved over complete geographical range of the host.
	- b.Increased death of the host with a single natural enemy alone.
	- c.Higher chances of introduced natural enemy to utilize other hosts when primary host population is low.
	- d.Invasion on all host stages (sequence theory).

Biological control could be controlled by adding and subtracting predators. Larval ectoparasitoids (e.g., Diglyphus spp.) and larval-pupal endoparasitoids (e.g., Chrysocharis oscinidis, Ganaspidium utilis) may interfere with each other when present in a cropping system. Larval ectoparasitoids which parasitize the leafminers, also indirectly harm the living endoparasitoid larva, already present in the leafminers, thus, leading to the death of the endoparasitoid. However, the endoparasitoids do not parasitize the leafminers with ectoparasitoids because if they do so, the parasitized hosts will not pupate, so the endoparasitoids can complete their life cycles. Therefore, numerous species may be needed to biologically control the leafminers in various crop systems.

	- 1.Turnbull and Chant [17] again gave the theory that single species introduction is best for biological control.
	- 2.To gain a desired level and effective biological control result of 2nd or 3rd natural enemy species are valuable.
	- 3.The lack of predictive theory is a major problem to implement biological control as the outcome of introduced natural enemy, with no prior history of classical biological control efforts, may not be assumed or predicted for new exotic species.
